Is it possible to trigger the D1 LED on the CarLoop GPS Sheild? It appears to be connected to pin D4 according to the schematic and I have tried using digitalWrite on D4 but it doesn't seem to work.
D4 is there to enable the LED but in order to switch it on the GPS module needs to provide the time pulse to the base of the transistor. I'd suspect you need a GPS fix for that to happen.
Thanks for the help ScruffR! It works and I get a yellow flash once GPS fixes and I get a time pulse once I send digitalWrite to high on D4.